The objective of this research is to further investigate the molecular species of formaldehyde present in the gas phase. Research by this investigator has found that the total formaldehyde content of vapors at equilibrium with a formalin solution consisted of methylene glycol, methylal and the first three oligomers of polyoxymethylene glycol monomethyl ethers. Utilized in the research was a novel gas phase trimethylsilylation procedure utilizing BSTFA with analysis of the TMS ethers by GC/FID. Further validation of the gas phase derivatization procedure is proposed through reaction of a series of low molecular weight alcohols and glycols with BSTFA in the gas phase and the products analyzed by GC/FID. Yields will indicate the feasibility of gas phase trimethylsilylation as a quantitative method of analysis for polyoxymethylene glycols and the glycol monomethyl ethers. A formaldehyde vapor generating system will then be constructed and the molecular species of formaldehyde produced will be analyzed by a matrix of procedures that, in combination, may distinguish between monomeric formaldehyde, s-trioxane and the polyoxymethylene glycols. Operating parameters of the generating system will be adjusted to obtain maximum monomeric formaldehyde production. Next, gas phase monomeric formaldehyde at known concentrations will be reacted with water vapor at several temperatures between 20 and 40 C in a dynamic dilution/reaction system and the products analyzed by the matrix of analytical procedures for formaldehyde and methylene glycol in order to calculate the gas phase equilibrium constant for the reaction. Results of this research will allow determination of the formaldehyde molecular species present in atmospheres (1) where human exposures occur; (2) utilized for animal exposures in toxicological assessment; and (3) in the humid airways of respiratory systems where carcinogenic effects have been observed.